DC to DC Chargers

Iain_U1250

Explorer
Nice, but lifpo4 will as you pull most of the times 1C charging (or more) if not regulated. Which will fry most people alternators, so I would not recommend giving this advice to anybody that has not matched their alternator output to their battery absorption profile. Even so, using elastic 4 stage charging is generally recommended for lithium batteries, and also GEL batteries if you follow the datasheet above it explains why...

Best case scenario you are damaging your cells.
View attachment 700424

I've seen the video about Lithium destroying alternators and all I can say that testing on my real truck with my 90A, 120A or 250A alternator that has not been the case at all. There were a few fundamental flaws in the way they did it, and i repeated their tests on my own system on an actual truck without coming close to burning out any of the alternators.

There is a bit of science in my system. The recommended charge current is 20-50A, with a maximum of 100A for my batteries. I have four batteries in parallel, so I am easily within the charging limits. If I had one small battery, then the 200A would exceed the recommend maximum charge current, but the BMS would trip out to proect that, but that may possibly damage the battery long term and worse it would not charge the battery. I've not seen many people who would only fit one battery into a truck, a caravan or camper trailer maybe, and also not many would match that to a 200+A alternator either, very few cars have 200A spare capacity in their alternator. I only fitted the 250A alternator as when driving at night with all the spotlights on, I can draw over 100A and wanted to make sure I was still able to charge the batteries. If you are designing a system, you just need to make sure you don't exceed the battery manufacturers limits.



I also spoke the manufacturers of the batteries, and they said they were designed as plug in replacements, with a proper BMS to manager overcharge/ discharge etc. I'm not sure about other brands but all Lithium systems need a proper BMS to protect them. I've never seen an input into the batteries of more than about 200A, and 200A was only when all the batteries were down to 20%. Normally it starts around 150A, with the current then steadily reducing down to 0A over a few hours of driving. The charge current for mine follows that graph, with the output of the alternator steadily dropping with time. System voltage starts around 13.2V and steadily builds to around 14.1V with 0 current - it is not flat like the graph, but then neither is the Victron Lithium battery charger, the voltage curve is not flat either, the actual voltage steadily rises whist current drops off.

I know that in the old days, the DC-DC chargera were touted as a means of getting maximum charge into a battery quicker, which did make a bit of sense if you were only driving for an hour or two, and had large battery banks but most people didn't use them. These daysa I would use one if I had a small lithium battery bank and a big alternator, but most people on camper trucks have a big battery bank and a small alternator. DC to DC chargers seem to be pretty unreliable bit of kit, so you would need some redundant ones as well. This is understandable as on a big battery bank they would be working to the maximum of their capacity all the time. Very few bits of consumer priced kit are rated for 100% capacity all the time.

I would also hate to limit my charging capacity to 30A or so, that would take forever to charge up 400Ah of batteries, I would need one for each battery.
 
Last edited:

Geo.Lander

Active member
I've seen the video about Lithium destroying alternators and all I can say that testing on my real truck with my 90A, 120A or 250A alternator that has not been the case at all. There were a few fundamental flaws in the way they did it, and i repeated their tests on my own system on an actual truck without coming close to burning out any of the alternators.

There is a bit of science in my system. The recommended charge current is 20-50A, with a maximum of 100A for my batteries. I have four batteries in parallel, so I am easily within the charging limits. If I had one small battery, then the 200A would exceed the recommend maximum charge current, but the BMS would trip out to proect that, but that may possibly damage the battery long term and worse it would not charge the battery. I've not seen many people who would only fit one battery into a truck, a caravan or camper trailer maybe, and also not many would match that to a 200+A alternator either, very few cars have 200A spare capacity in their alternator. I only fitted the 250A alternator as when driving at night with all the spotlights on, I can draw over 100A and wanted to make sure I was still able to charge the batteries. If you are designing a system, you just need to make sure you don't exceed the battery manufacturers limits.



I also spoke the manufacturers of the batteries, and they said they were designed as plug in replacements, with a proper BMS to manager overcharge/ discharge etc. I'm not sure about other brands but all Lithium systems need a proper BMS to protect them. I've never seen an input into the batteries of more than about 200A, and 200A was only when all the batteries were down to 20%. Normally it starts around 150A, with the current then steadily reducing down to 0A over a few hours of driving. The charge current for mine follows that graph, with the output of the alternator steadily dropping with time. System voltage starts around 13.2V and steadily builds to around 14.1V with 0 current - it is not flat like the graph, but then neither is the Victron Lithium battery charger, the voltage curve is not flat either, the actual voltage steadily rises whist current drops off.

I know that in the old days, the DC-DC chargera were touted as a means of getting maximum charge into a battery quicker, which did make a bit of sense if you were only driving for an hour or two, and had large battery banks but most people didn't use them. These daysa I would use one if I had a small lithium battery bank and a big alternator, but most people on camper trucks have a big battery bank and a small alternator. DC to DC chargers seem to be pretty unreliable bit of kit, so you would need some redundant ones as well. This is understandable as on a big battery bank they would be working to the maximum of their capacity all the time. Very few bits of consumer priced kit are rated for 100% capacity all the time.

I would also hate to limit my charging capacity to 30A or so, that would take forever to charge up 400Ah of batteries, I would need one for each battery.
I feel that, I am looking at 12.5 hours for a full 10kw charge with duel Orion units (800w). But Most people do not have 250A alternators, I am changing mine for a 100A one but anything bigger I would need to up-rate my belts, pulleys etc (I have been told and read on this forum)..,
My batteries will pull 0.5C (100A @ 24VDC being 200aH capacity) *2 so would total my alternator, I think most are in the same boat..

You should not relay on BMS to trigger overcharge protection, yes it is needed but when you trigger the BMS overcharge you have to manually disable if in most cases. The BMS overcharge and under voltage cut-offs are not designed to be used as common charging regulator, at least in the BMSs I have tested.
 

Iain_U1250

Explorer
I feel that, I am looking at 12.5 hours for a full 10kw charge with duel Orion units (800w). But Most people do not have 250A alternators, I am changing mine for a 100A one but anything bigger I would need to up-rate my belts, pulleys etc (I have been told and read on this forum)..,
My batteries will pull 0.5C (100A @ 24VDC being 200aH capacity) *2 so would total my alternator, I think most are in the same boat..

You should not relay on BMS to trigger overcharge protection, yes it is needed but when you trigger the BMS overcharge you have to manually disable if in most cases. The BMS overcharge and under voltage cut-offs are not designed to be used as common charging regulator, at least in the BMSs I have tested.
I agree, that's why I fitted a 14.5V regulator, the maximum charge voltage is 15V, so that should be a fair safety margin. Under voltage is something I get an alarm on Victron battery monitor, so when I get close, it will beep like mad.

I run a dual belt pulley on my Alternator /Aircon but I have seen people running a lot more than I do off a single belt, but not sure how long it would last.
 

Alloy

Well-known member
I've seen the video about Lithium destroying alternators and all I can say that testing on my real truck with my 90A, 120A or 250A alternator that has not been the case at all. There were a few fundamental flaws in the way they did it, and i repeated their tests on my own system on an actual truck without coming close to burning out any of the alternators.

There is a bit of science in my system. The recommended charge current is 20-50A, with a maximum of 100A for my batteries. I have four batteries in parallel, so I am easily within the charging limits. If I had one small battery, then the 200A would exceed the recommend maximum charge current, but the BMS would trip out to proect that, but that may possibly damage the battery long term and worse it would not charge the battery. I've not seen many people who would only fit one battery into a truck, a caravan or camper trailer maybe, and also not many would match that to a 200+A alternator either, very few cars have 200A spare capacity in their alternator. I only fitted the 250A alternator as when driving at night with all the spotlights on, I can draw over 100A and wanted to make sure I was still able to charge the batteries. If you are designing a system, you just need to make sure you don't exceed the battery manufacturers limits.



I also spoke the manufacturers of the batteries, and they said they were designed as plug in replacements, with a proper BMS to manager overcharge/ discharge etc. I'm not sure about other brands but all Lithium systems need a proper BMS to protect them. I've never seen an input into the batteries of more than about 200A, and 200A was only when all the batteries were down to 20%. Normally it starts around 150A, with the current then steadily reducing down to 0A over a few hours of driving. The charge current for mine follows that graph, with the output of the alternator steadily dropping with time. System voltage starts around 13.2V and steadily builds to around 14.1V with 0 current - it is not flat like the graph, but then neither is the Victron Lithium battery charger, the voltage curve is not flat either, the actual voltage steadily rises whist current drops off.

I know that in the old days, the DC-DC chargera were touted as a means of getting maximum charge into a battery quicker, which did make a bit of sense if you were only driving for an hour or two, and had large battery banks but most people didn't use them. These daysa I would use one if I had a small lithium battery bank and a big alternator, but most people on camper trucks have a big battery bank and a small alternator. DC to DC chargers seem to be pretty unreliable bit of kit, so you would need some redundant ones as well. This is understandable as on a big battery bank they would be working to the maximum of their capacity all the time. Very few bits of consumer priced kit are rated for 100% capacity all the time.

I would also hate to limit my charging capacity to 30A or so, that would take forever to charge up 400Ah of batteries, I would need one for each battery.
Did you check if the alternator is running below 250F / 120C at FLA. It can go over that but will wear out faster.
 

Iain_U1250

Explorer
Did you check if the alternator is running below 250F / 120C at FLA. It can go over that but will wear out faster.
I used a IR gun and checked the 250A alternator a couple of times when on a long run, sits at around 85-95C, so not a problem. It probably gets a fair amount of air flow even though I have blocked off the grill directly in front to of it as it is a fair way off to the side of the engine.

2020-11-17 08.39.57.jpg


The 90A sit under the exhaust manifold, and that sits around 95-105C, and that is more of less freewheeling as it only charges the starter battery. Next time we do a long night run, I'll check it again, as it will have been pulling +150A for a long time. The worst situation would be doing a night drive with all spotlights on, and having to charge the batteries, then the alternator will be producing close to maximum output all the time. Have not tested that yet.

On my Bentley, that alternator is water cooled, and the engine runs normally at 95-105C, so the coils on the alternator will be a fair bit higher than that. It is only a 190A alternator, but it sits right in front of the turbo, and gets almost no airflow, doesn't even have a fan. The alternator is on the bottom left. I guess the little fans on the alternator do make quite a difference, the Mechman alternator has a fan behind the fancy machined front end.

directbelt.jpg
 
Last edited:

Neil

Observer
I've seen the video about Lithium destroying alternators and all I can say that testing on my real truck with my 90A, 120A or 250A alternator that has not been the case at all
I think I have seen this video to. If its the same one it is flawed test .

The tester claimed that the Alternator wasn't going fast enough to keep cool and simply overheated and burnt out.

However of you look at thectest he has the alternator being powered by a belt and pully on an electric motor. The ratio between motor and alternator looks to be near 1 :1

This would never happen in real.life if your picking your belt drive up from the much larger crank pulley

It was a terrible test

Neil
 

Iain_U1250

Explorer
I think I have seen this video to. If its the same one it is flawed test .

The tester claimed that the Alternator wasn't going fast enough to keep cool and simply overheated and burnt out.

However of you look at thectest he has the alternator being powered by a belt and pully on an electric motor. The ratio between motor and alternator looks to be near 1 :1

This would never happen in real.life if your picking your belt drive up from the much larger crank pulley

It was a terrible test

Neil
My thoughts exactly Neil, I have a 2.4:1 ratio on mine, and found that at idle, the alternator didn't put out much current at all, despite the what the video says, the alternator didn't even get warm really. It only got hotter when I upped the RPM to 1800rpm and the alternators were at max capacity. I have looked at getting a smaller pulley for the alternator, but will have to get one custom made to fit, which proved to be pretty difficult and expensive, and to be honest, the bigger pulleyworks fine when driving, which would normally be around 1700-2000rpm, it just doesnt get me much over 200A.
 

Alloy

Well-known member
I used a IR gun and checked the 250A alternator a couple of times when on a long run, sits at around 85-95C, so not a problem. It probably gets a fair amount of air flow even though I have blocked off the grill directly in front to of it as it is a fair way off to the side of the engine.

View attachment 700582


The 90A sit under the exhaust manifold, and that sits around 95-105C, and that is more of less freewheeling as it only charges the starter battery. Next time we do a long night run, I'll check it again, as it will have been pulling +150A for a long time. The worst situation would be doing a night drive with all spotlights on, and having to charge the batteries, then the alternator will be producing close to maximum output all the time. Have not tested that yet.

On my Bentley, that alternator is water cooled, and the engine runs normally at 95-105C, so the coils on the alternator will be a fair bit higher than that. It is only a 190A alternator, but it sits right in front of the turbo, and gets almost no airflow, doesn't even have a fan. The alternator is on the bottom left. I guess the little fans on the alternator do make quite a difference, the Mechman alternator has a fan behind the fancy machined front end.

View attachment 700581
Looks like the alternator has a machined alum body. Very nice. Who makes it?

When I can't get the right size pulley I find something with a smaller bore (or blind bore) so I can bore it and broach the keyway........20 years ago one could get it done for a case of beer. There use to be as many machine shops as there are cell phone repair shops now :)
 

Iain_U1250

Explorer
Looks like the alternator has a machined alum body. Very nice. Who makes it?

When I can't get the right size pulley I find something with a smaller bore (or blind bore) so I can bore it and broach the keyway........20 years ago one could get it done for a case of beer. There use to be as many machine shops as there are cell phone repair shops now :)
It is a Mechman - https://www.mechman.com/alternators/e-series-billet-250a-alt-fits-6-12-cs144-machined-finish/ but asked for black not silver
 

Darwin

Explorer
There is an easier, and more simple solution you might try out. It's how I set mine up. This is what I did. Mount 1000 watt inverter in truck cab and run the cables off of the truck chassis batteries. Next, Run 120 volt extension cord to your 'house' inverter AC input. This charges the 'house' batteries to however you have your camper inverter charger programmed. With the charging set up this way, the 'house' batteries act as though they are hooked up to shore power, but really it is the second inverter off the truck chassis batteries that is providing the charge current to inverter/charger in the camper. I limit the input current on the victron inverter charger so as not to draw too much from the truck chassis inverter/batteries. I have a 250 amp alternator BTW.
 

Geo.Lander

Active member
There is an easier, and more simple solution you might try out. It's how I set mine up. This is what I did. Mount 1000 watt inverter in truck cab and run the cables off of the truck chassis batteries. Next, Run 120 volt extension cord to your 'house' inverter AC input. This charges the 'house' batteries to however you have your camper inverter charger programmed. With the charging set up this way, the 'house' batteries act as though they are hooked up to shore power, but really it is the second inverter off the truck chassis batteries that is providing the charge current to inverter/charger in the camper. I limit the input current on the victron inverter charger so as not to draw too much from the truck chassis inverter/batteries. I have a 250 amp alternator BTW.
A little bit of genius there! If you don't mind the conversion inefficiencies :D Good inverters are expensive too thou, and power is power so you need to make sure you alternator can manage, genius thou!
 

DiploStrat

Expedition Leader
A little bit of genius there! If you don't mind the conversion inefficiencies :D Good inverters are expensive too thou, and power is power so you need to make sure you alternator can manage, genius thou!
AEON claim to be doing this on their new van. Partly, perhaps, as a way to charge a 24v battery. Bank. But it seems to me that the losses of two inverters must be serious. I defer to those who actually know what they are talking about.
 

DaveInDenver

Luddite
AEON claim to be doing this on their new van. Partly, perhaps, as a way to charge a 24v battery. Bank. But it seems to me that the losses of two inverters must be serious. I defer to those who actually know what they are talking about.
This isn't really two inverters. It's one inverter that feeds the mains side of the house inverter, which is presumably really just a 120/240V powered battery charger/maintainer inside that happens to have another inverter connected to the battery.

Then it's the same as a DC-DC charger in the most basic form, converting from DC to AC and back to DC. You could also just use any battery charger designed to run from the mains in this case.

The overall losses are likely to be higher than a dedicated DC-DC charger mainly because the device won't benefit from being engineered to run all stages at best efficiencies per the task.

You can just check the datasheets.

For example a Samlex SA-1000K is full load efficient at 89% (for a 12V version) and 92% (24V). It'll be a little higher at partial load, sometimes as much as 5% at 1/2 rated load. Call it 90% on average.


Fed into a charger. This isn't necessarily a simple calculation, but it's possible to ball park. An Iota DLS is stated as >80% and a Noco or BatteryMINDr will probably just say it meets CA CEC rules. So that'll work out to about 89% or greater in plain numbers for active mode charging.

Compare this to a perhaps a Victron Orion, which are stated to be between 85% to 89% efficient depending on configuration.

https://www.victronenergy.com/uploa...DC-DC-converters-isolated-100-250-400W-EN.pdf

So the difference isn't show stopping, maybe on the order of 5% or 10% worse losses using separate inverter and charger. In this case of a running engine alternator feeding the system the penalty isn't even really significant. It's not going to mean much difference in alternator temperature or engine load.

The trade-offs are convenience of an all-in-one solution verses multiple device and wiring. But then again having a separate inverter and charger gives you flexibility and would be easier to repair.

Where inverter efficiency is important is when the engine is not running. A few percentage points there might translate to significant changes in run times. Same with a charger to some extent. A higher efficiency charger that draws down your solar system less is important. But a few percent worse when skimmed from a 250A diesel engine-driven alternator might mean you go from 12.00 to 11.95 MPG on your trip.
 
Last edited:

DiploStrat

Expedition Leader
"This isn't really two inverters. It's one inverter that feeds the mains side of the house inverter, which is presumably really just a 120/240V powered battery charger/maintainer inside that happens to have another inverter connected to the battery."

Duh! Thank you. That makes a LOT of sense. Of course, the second inverter/charger has to be on, it it will have idling losses (+ whatever loads may be on).

Based on anecdotal evidence with my 800Ah DIY lithiun-iron bank, there may also be a few advantages to feeding with a single charger. I think I see some evidence of dueling chargers that I never saw with lead acid. Possibly an artifact of the very flat voltages of lithium iron batteries.

Many thanks.
 
Top